Projection-exposure apparatus for manufacturing semiconductor elements, liquid crystal display elements, and the like, tend to be large and bulky, and require a large area of floor space for their installation. Such exposure apparatus generally employ mercury lamps, laser light sources, or the like as light sources. Laser light sources, particularly excimer laser light sources, are extremely large compared to light sources such as mercury lamps. Accordingly, particularly with exposure apparatus employing excimer laser light sources, it is necessary to arrange the light source separately from the exposure apparatus main assembly. To allow effective utilization of clean room floor space, the excimer laser light source is sometimes installed on a floor level beneath the floor of the clean room housing the exposure apparatus. Such lower rooms frequently have a lower cleanliness rating.
A projection-exposure apparatus typically employs an optical integrator to uniformly illuminate the mask. The optical integrator must be illuminated with high efficiency by light from the light source. However, where an excimer laser light source and an exposure apparatus main assembly are installed on different floor levels, floor deformation and displacement of one floor level relative to the other floor level can cause misalignment of the light beam that illuminates the optical integrator. Such misalignment results in reduced illuminance and reduced uniformity of the illuminance profile at the photosensitive substrate (i.e., the surface being exposed).
In an alternative clean room arrangement, an excimer laser light source and an associated exposure apparatus main assembly are sometimes secured to a "grating" or the like installed some distance above a common floor, wherein a space located between the floor and the grating are utilized for plumbing and other utilities. In such cases, deformation or other displacement of the grating, which tends to be more easily deformed than a floor, can cause misalignment of the light beam that illuminates the optical integrator, resulting in reduced illuminance, and reduced uniformity of the illuminance profile, at the photosensitive substrate. It is desirable to avoid such deleterious effects. Effective utilization of any space between the excimer laser light source and the exposure apparatus main assembly (supported on a grating by the same floor system) is also desirable.